Matrices & Determinants
Transpose and symmetric matrices
Grade Class 12

Question:

A and B are two given matrices such that the order of A is 3 × 4 , if A' B and BA' are both defined then
(A) order of B' is 3 × 4
(B) order of B'A is 4 × 4
(C) order of B'A is 3 × 3
(D) B'A is undefined

Step-by-Step Solution

Key Concept: If A is 3x4, then A' is 4x3. For A'B to be defined, B must be 3xn. For BA' to be defined, B must be mx4. Thus B must be 3x4. Then B' is 4x3. B'A is (4x3) * (3x4) = 4x4.
Given order of A is 3 \times 4, so order of A' is 4 \times 3. For A'B to be defined, B must be of order 3 \times n. For BA' to be defined, B must be of order m \times 4. Comparing these, B must be of order 3 \times 4. Then B' is of order 4 \times 3. Thus, B'A is (4 \times 3) \times (3 \times 4) = 4 \times 4.
Correct Answer: 2

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